feat(client): use futures stream to speed up downloads

[RolandSherwin]

Description

Summary generated by Reviewpad on 08 Jan 24 18:39 UTC

This pull request contains the following changes:

In the error.rs file:

• Added a new variant EmptyDataMap to the Error enum. This variant represents the error of an empty data map being provided.

In the sn_client/src/files/mod.rs file:

• The chunks module is now importing only the Error type from the self_encryption module, instead of the DataMapLevel and SmallFile types.
• Removed the import of futures::{future::join_all, stream::FuturesOrdered, StreamExt}.
• Removed the import of itertools::Itertools.
• Modified the import of self_encryption::{self, decrypt_full_set, ChunkInfo, DataMap, EncryptedChunk, StreamSelfDecryptor, MIN_ENCRYPTABLE_BYTES}. Removed the decrypt_full_set function and types ChunkInfo, DataMap, EncryptedChunk, and StreamSelfDecryptor. Only the MIN_ENCRYPTABLE_BYTES constant remains.
• Removed the import of std::time::Instant.
• Removed the import of tokio::task.
• Removed the import of tracing::trace.
• Removed the import of xor_name::XorName.
• Removed several methods of the FilesApi implementation, including read_from, read_all, unpack_chunk, seek, and try_get_chunks.